# lecture7 - Chapter Chapter 9 Phase Diagrams 1 Phase...

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Chapter 9 Phase Diagrams se g s 1

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Phase Diagrams ISSUES TO ADDRESS. .. When we combine two elements. .. what equilibrium state do we get? In particular, if we specify. .. -- --a composition (e.g., wt% Cu a composition (e.g., wt% Cu - wt% Ni), and wt% Ni), and -- --a temperature ( a temperature ( T ) then. .. How many phases do we get? What is the composition of each phase? How much of each phase do we get? Phase B Phase A Nickel atom Copper atom
Phase Diagrams Example: The H 2 O ….Unary (1-component )System

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Phase Diagrams Example: The Carbon Unary (1-component ) System) From: F.P. Bundy, The P,T Phase and Reaction diagram for elemental Carbon, 1979; J. Geophys. Res. 85 (B12) (1980) 6930.
Phase Diagrams Example: The Carbon Dioxide Unary (1-component ) System)

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Multi Multi-component Phase Diagrams component Phase Diagrams What we will study in this lecture… The Fe-C system (Iron, Steel and Cast Irons)
Phase Phase Equilibria Equilibria: Solubility Limit : Solubility Limit Introduction – Solutions – solid solutions, single phase – Mixtures – more than one phase olubility Limit Sucrose/Water Phase Diagram olubility 10 0 Solubility Limit : Max concentration for which only a single phase lution occurs ture (°C) Solubility Limit L (liquid) + 60 80 solution occurs. Question: What is the solubility limit at 20°C ? Tempera L (liquid solution i.e., syrup) S (solid sugar) 20 40 Answer: 65 wt% sugar . If C o < 65 wt% sugar: syrup 65 t% 65 ure ugar 0 20 40 60 80 100 C o =Composition (wt% sugar) ater If C o > 65 wt% sugar: syrup + sugar. Pu Su W

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Components and Phases Components : The elements or compounds which are present in the mixture g Al and Cu) (e.g., Al and Cu) Phases : The physically and chemically distinct material regions t lt that result (e.g., a and b). Aluminum- opper b (lighter Copper Alloy a (darker phase) phase)
Effect of T & Composition ( C o ) Changing T can change # of phases: path A to B . Changing C o can change # of phases: path B to D . D (100°C,90) 2 phases B (100°C,70) 1 phase 100 re (°C) 0 80 L (liquid) + water- mperatu r L ( liquid solution i.e., syrup) 40 60 S (solid sugar) sugar system A (20°C,70) 2 phases 0 0 00 0 0 0 Te m 20 0 70 80 100 60 40 20 0 C o =Composition (wt% sugar)

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Phase Phase Equilibria Equilibria Simple solution system (e.g., Ni-Cu solution) Crystal Structure Electro- negativity r (nm) Ni FCC 1.9 0.1246 Cu FCC 1.8 0.1278 Both have the same crystal structure (FCC) and have similar electronegativities and atomic radii ( W. Hume – Rothery rules ) suggesting high mutual solubility. Ni and Cu are totally miscible in all proportions.
Phase Diagrams Indicate phases as function of T , C o , and P . For this course: inary systems: just 2 components -binary systems: just 2 components. -independent variables: T and C o ( P = 1 atm is almost always used). 2 phases: 600 T (°C) Phase Diagram for Cu-Ni • 2 phases: L (liquid) (FCC solid solution) 1500 1600 L (liquid) system • 3 phase fields: L L + 1300 1400 1100 1200 a (FCC solid wt% Ni 20 40 60 80 100 0 1000 solution)

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Phase Diagrams : d t f h # and types of phases Rule 1: If we know T and C o , then we know: --the # and types of phases present.
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lecture7 - Chapter Chapter 9 Phase Diagrams 1 Phase...

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